Field of the Disclosure
The present disclosure relates to sensors, and more specifically, to high-dynamic range sensors.
Background
An imaging system depends on an image sensor to generate an electronic representation of a visual image. Examples of image sensors include charge coupled device (CCD) image sensors and active pixel sensor (APS) devices. Typically, these images sensors include a plurality of light sensitive elements (sensels) arranged in a regular pattern of rows and columns. The signal generated by each sensel represents the amount of light incident upon the area corresponding to that sensel.
The dynamic range of these image sensors is typically limited by the amount of charge that can be collected and held for a given sensel. Thus, if the incident light is very bright and creates more electrons than can be held by that sensel, the light represented by those excess electrons is lost. For example, a modern image sensor, limited by characteristics such as electron capacity and electron readout noise, can detect about 14 stops of dynamic range for each sensel (i.e., it takes 14 doublings of the smallest recordable value to reach saturation).
Accordingly, an image sensor that can provide a wider dynamic range than the dynamic range provided by the conventional image sensor is desirable. For example, when capturing scenes that include drastic changes in brightness, if the exposure is made to ensure there is enough signal in the dark areas, the areas with stronger light will saturate the sensels, and the actual light radiance for those saturated elements cannot be obtained. Accordingly, sensors with higher dynamic range are needed for capturing such scenes.